Traumatic brain injury (TBI) is an epidemic in the United States with survivors often having many decades of productive life loss. An estimated 5.3 million Americans currently live with disabilities resulting from TBI. Despite the fact that about 25% of the population with TBI are women, the large majority of clinical and animal research on TBI to date has been with males. Evidence shows that females have more difficulties with post-concussive symptoms and poorer outcome after TBI compared to males. It is suspected that dopamine I (DA) plays a crucial role in working memory and other aspects of executive functioning, and decreases in DA system function after TBI are thought to affect cognitive recovery. Estrogen is well known to play a significant role in dopaminergic functioning, and estrogen has been shown to have a neuroprotective effect acutely after TBI. However, no one has evaluated the effect of estrogen on DA functioning and cognitive recovery from TBI. The goal of this proposal is to evaluate the effects of estrogen on DA pathways in female rodents compared to male rodents after TBI. The effects of methylphenidate on cognitive performance and DA function in females and male rodents after experimental TBI will also be studied. The long-term goal is to delineate the role of estrogen on DA system mediated cognitive deficits in order to develop and optimize new and existing therapies that specifically target and enhance recovery of both males and females after TBI.